In current vehicles, various vehicle-mounted devices are mounted for enabling a driver to drive comfortably and safely. For example, a navigation system (hereinafter referred to as “navigation system”) for guiding a driving direction to a destination and an audio equipment for reproducing music are mounted in the vehicle. In order to operate the vehicle-mounted devices, it is necessary that the driver sets the destination and the music for the devices. In order to facilitate the setting operation, a technique in which a display screen is mounted at a position where the driver can easily see in a vehicle interior, and various information on the setting operation is displayed on the display screen has been widespread.
When the setting operation of the vehicle-mounted devices is performed while the vehicle is traveling, the driving operation may be hindered. Under the circumstances, while the vehicle is traveling, the operation of setting the vehicle-mounted device by the driver is not accepted, and an image on the display screen is displayed on a mode (for example, luminance or contrast is lowered) different from a normal mode. Because the driver performs the setting operation while checking the display screen, if the display screen is different in the display mode from the normal display screen, the driver can immediately recognize that the setting operation is not accepted (Patent Literature 1).
However, there arises such an issue that even after the display screen has been changed to the display mode different from the normal mode in association with the travel start of the vehicle, there is a tendency for the driver to continue the operation of the vehicle-mounted device for a while. This is because, even though the driver is aware that the display mode has been switched to another during the operation of setting the device and recognizes that the setting operation is no longer enabled, the driver cannot immediately accept that the setting operation is interrupted in a halfway state.
In addition, the same situation can occur even when the display mode indicating that the vehicle-mounted device cannot be operated has been switched to the normal display mode indicating that the vehicle-mounted device can be operated in association with a fact that the vehicle-mounted device becomes operable, for example, the vehicle stops. In other words, aside from a case in which the driver is waiting for the vehicle-mounted device to become operable, normally, the driver thinks of operating or recalls the content of the interrupted operation after the driver is aware that the vehicle-mounted device becomes operable. Therefore, it takes a long time to actually start the operation.